Gas turbines are increasingly being equipped with multiple burner systems. The liquid fuels are injected in this case into the burner systems by using complex atomizer nozzles. Within the scope of the attempts to optimize the combustion quality with respect to the emissions and the efficiency, it is necessary for these parameters to satisfy ever more stringent quality requirements with reference to the spray quality in the case of modern gas turbine atomizers. Stationary gas turbines are operated with a wide range of liquid fuel qualities. These fuels, for example heating oil of "extra light" quality, tend to form residues when vaporized (coking).
If a gas turbine operated with liquid fuel is shut down, the fuel injection systems heat up via the convective thermal flux of the surrounding material to such an extent that such residues can form if the fuel systems situated in the region of the thermal block have not been completely emptied of fuel. These hard residues worsen the atomizer quality to an inadmissible extent, and lead to rising through-flow resistances of the nozzles. The gas turbine can no longer be operated in the advanced stage of formation of residues.
Over and above the problem of coking, after the shutdown of a gas turbine operated with liquid fuel there is also the risk of the fuel passing from the fuel systems in an uncontrolled fashion into the combustion chamber when the rotor is stationary, or into the boiler possibly connected downstream of the gas turbine and forming an explosive mixture there with air at rest.
In order to avoid the problems described, the liquid fuel must be removed from the fuel systems in a controlled process after shutting down the gas turbine.